(a) Field of the Invention
The present invention relates to a signal converting device in a wireless communication system and a receiving device using the same.
(b) Description of the Related Art
A receiving device of a wireless communication system receives radio frequency signals from a transmitting device through an antenna to filter them, amplify them, frequency-convert them, and convert them into analog to digital signals. In this instance, frequency conversion represents a process for converting the radio frequency signal into a baseband frequency or an intermediate frequency (IF) by using a frequency down converter.
The frequency down converter combines an input signal and a local oscillator's signal to generate a baseband frequency signal corresponding to the frequency difference between the two signals. However, when the local oscillator's signal appears as a leakage signal to the frequency down converter's output, it can worsen the entire linearity of the receiving device of the wireless communication system. Therefore, a double balance frequency converter is generally used for the frequency down converter in order to minimize leakage of the local oscillation signal. The double balance frequency converter has a circuit structure of using differential signals.
However, in the receiving device of the wireless communication system, the antenna for directly receiving the radio frequency signals is generally designed to process single ended signals because of size and cost. Hence, the radio frequency signal is required to be converted from the single ended signal to the differential signal before it is input to the frequency down converter.
For this purpose, various differential signal converting devices are additionally inserted into the receiving device of the wireless communication system. However, the addition of such differential signal converting devices increases current consumption of the receiving device, degrades noise figure and linear characteristic at a receiving terminal, and increases size and cost of the receiving device.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.